Re: [time-nuts] Why are 1PPS signals so skinny?
The LED current could also be switched with a very long rise/fall time so that there isn't any transient, in the abrupt sense of the word. Who's gonna see the difference? Tom Holmes, N8ZM Tipp City, OH EM79 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Wednesday, May 16, 2012 10:57 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 05/16/2012 02:21 PM, shali...@gmail.com wrote: It would be very easy to use a constant current to drive the LED and simply short it periodically to provide the blinking without supply current variations. You would still have short transients in the drive circuit, but these should be much easier to filter. Agreed. You could also have a pair of LEDs and alternate which of them is lit. Then, to reduce the impact on the PPS signals, the LED on/off could be forced to be phase-shifted to the PPS. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny
On 05/17/2012 05:38 AM, Tom Holmes wrote: The LED current could also be switched with a very long rise/fall time so that there isn't any transient, in the abrupt sense of the word. Who's gonna see the difference? In a group that has GPS synchronized clock hands? HERESY! :) Tom Holmes, N8ZM Tipp City, OH EM79 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
As most PSs for digital circuitry include a regulator, it's output impedance at 1Hz is low enough to filter most out of it - see the load transient response diagram of the used regulator - as the open loop gain of the regulator's internal error amplifier at such a low frequency is practically equal to that of DC gain. While the 1Hz component is of no concern (power consumption left aside), the fast edges pose a higher demand on proper decoupling. On 5/15/2012 9:45 PM, shali...@gmail.com wrote: The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. At 1Hz, the power supply filters nothing. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mike Smi...@flatsurface.com Sender: time-nuts-boun...@febo.com Date: Mon, 14 May 2012 20:44:04 To:time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 5/14/2012 8:21 PM, Tom Van Baak wrote: one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. How does a short pulse help? It's still tens of watts every second, but instead of lasting 0.5 seconds, it lasts 0.5 seconds. Less power used overall, but still the same sudden change on the second. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 05/16/2012 05:25 AM, Hal Murray wrote: rich...@karlquist.com said: FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Why should lights blink when they are happy? Your eye is real good at noticing blinking things. Why not use blinking for things that are broken and need attention? Of course, with a PPS, blinking is an obvious thing to do: 1 resistor, 1 LED, your eye does all the work. I built a converter from blink on happy to blink on sad. I've been happy with it. If you have a timer trigger that invert the LED drive, when it gets stuck for whatever reason, then you will notice the lack of blinking. This is why happy blinking is being used. It's really a form of simple software debugging tool in its simplest form. You could get a watchdog timer that would trigger an unhappy blinker. More hardware. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
It would be very easy to use a constant current to drive the LED and simply short it periodically to provide the blinking without supply current variations. You would still have short transients in the drive circuit, but these should be much easier to filter. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Magnus Danielson mag...@rubidium.dyndns.org Sender: time-nuts-boun...@febo.com Date: Wed, 16 May 2012 09:51:00 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 05/16/2012 05:25 AM, Hal Murray wrote: rich...@karlquist.com said: FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Why should lights blink when they are happy? Your eye is real good at noticing blinking things. Why not use blinking for things that are broken and need attention? Of course, with a PPS, blinking is an obvious thing to do: 1 resistor, 1 LED, your eye does all the work. I built a converter from blink on happy to blink on sad. I've been happy with it. If you have a timer trigger that invert the LED drive, when it gets stuck for whatever reason, then you will notice the lack of blinking. This is why happy blinking is being used. It's really a form of simple software debugging tool in its simplest form. You could get a watchdog timer that would trigger an unhappy blinker. More hardware. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
But if the LED transition was offset any significant amount of time from the PPS, you wouldn't be able to use it to set your watch! Dave :-) On Wed, May 16, 2012 at 10:57 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Then, to reduce the impact on the PPS signals, the LED on/off could be forced to be phase-shifted to the PPS. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 05/16/2012 07:42 PM, Dave Martindale wrote: But if the LED transition was offset any significant amount of time from the PPS, you wouldn't be able to use it to set your watch! Dave :-) Well, the offset compensates for the protein computer delay. Cheers, Magnus On Wed, May 16, 2012 at 10:57 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Then, to reduce the impact on the PPS signals, the LED on/off could be forced to be phase-shifted to the PPS. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
I always thought it was nice to have the pretty LEDs showing the power supplies are working, but then you have to find the one that's not lit. I've seen others that have a 'fail' indicator, but if the power supply is dead, what powers the fail LED. The B-1B test stations have an interface board with status LEDs behind a smoked plexiglass door. One version of the CCA has the 90° LEDs facing backwards. Mike On 5/15/2012 10:25 PM, Hal Murray wrote: rich...@karlquist.com said: FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Why should lights blink when they are happy? Your eye is real good at noticing blinking things. Why not use blinking for things that are broken and need attention? Of course, with a PPS, blinking is an obvious thing to do: 1 resistor, 1 LED, your eye does all the work. I built a converter from blink on happy to blink on sad. I've been happy with it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. At 1Hz, the power supply filters nothing. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mike S mi...@flatsurface.com Sender: time-nuts-boun...@febo.com Date: Mon, 14 May 2012 20:44:04 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 5/14/2012 8:21 PM, Tom Van Baak wrote: one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. How does a short pulse help? It's still tens of watts every second, but instead of lasting 0.5 seconds, it lasts 0.5 seconds. Less power used overall, but still the same sudden change on the second. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
The Thunderbolt's output impedance is much less than 10 ohms. However, it is only necessary to filter the end of the line for a clean pulse. See http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.php I used the Thunderbolt's PPS output as a source in those measurements. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Said Jackson saidj...@aol.com Sender: time-nuts-boun...@febo.com Date: Mon, 14 May 2012 19:02:51 To: Tom Van Baakt...@leapsecond.com; Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Discussion of precise time and frequency measurementtime-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? These types of pulses should be routed as open-ended source-terminated reflected wave switched transmission lines. Power will only flow for nanoseconds as the pulse travels over the line. There won't be a drop of 50% of the voltage at the target and no large power spikes in the unit or requirements for proper impedance matching at the receiver side. Some units like the thunderbolt look quite bad driving a 50 ohms transmission line, others that are designed with proper 50 ohms series impedance create a sharp nice signal. Bye, Said Sent from my iPad On May 14, 2012, at 17:21, Tom Van Baak t...@leapsecond.com wrote: Mark, I too once preferred 50% duty cycle 1 Hz signals because they seemed more natural. But one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. When a dozen DUT generate 1PPS along with as many REF pulses (via cascaded pulse distribution amps) and then these all go to both inputs of a TIC and there's also LED's on both TIC channels as well as the dist amps, the net load is enormous. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. Remember 5V into 50R is 0.1 Amps. That was a modest amount of current in the 1950's, but massive overkill today. So that's why I now prefer short (e.g., 1 ms or 10 us) pulses. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Came to this thread late. Could it be thin because the end output of even a synchronous dividing chain needs to be resynced to the beginning to maintain phase? Don shali...@gmail.com The Thunderbolt's output impedance is much less than 10 ohms. However, it is only necessary to filter the end of the line for a clean pulse. See http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.php I used the Thunderbolt's PPS output as a source in those measurements. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Said Jackson saidj...@aol.com Sender: time-nuts-boun...@febo.com Date: Mon, 14 May 2012 19:02:51 To: Tom Van Baakt...@leapsecond.com; Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Discussion of precise time and frequency measurementtime-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? These types of pulses should be routed as open-ended source-terminated reflected wave switched transmission lines. Power will only flow for nanoseconds as the pulse travels over the line. There won't be a drop of 50% of the voltage at the target and no large power spikes in the unit or requirements for proper impedance matching at the receiver side. Some units like the thunderbolt look quite bad driving a 50 ohms transmission line, others that are designed with proper 50 ohms series impedance create a sharp nice signal. Bye, Said Sent from my iPad On May 14, 2012, at 17:21, Tom Van Baak t...@leapsecond.com wrote: Mark, I too once preferred 50% duty cycle 1 Hz signals because they seemed more natural. But one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. When a dozen DUT generate 1PPS along with as many REF pulses (via cascaded pulse distribution amps) and then these all go to both inputs of a TIC and there's also LED's on both TIC channels as well as the dist amps, the net load is enormous. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. Remember 5V into 50R is 0.1 Amps. That was a modest amount of current in the 1950's, but massive overkill today. So that's why I now prefer short (e.g., 1 ms or 10 us) pulses. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Simply dividing the 10MHz by a binary counter and taking the most significant bit for the PPS leads to a 161.1391mS pulse. On Tue, May 15, 2012 at 9:26 PM, Don Latham d...@montana.com wrote: Came to this thread late. Could it be thin because the end output of even a synchronous dividing chain needs to be resynced to the beginning to maintain phase? Don shali...@gmail.com The Thunderbolt's output impedance is much less than 10 ohms. However, it is only necessary to filter the end of the line for a clean pulse. See http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.php I used the Thunderbolt's PPS output as a source in those measurements. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Said Jackson saidj...@aol.com Sender: time-nuts-boun...@febo.com Date: Mon, 14 May 2012 19:02:51 To: Tom Van Baakt...@leapsecond.com; Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Discussion of precise time and frequency measurementtime-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? These types of pulses should be routed as open-ended source-terminated reflected wave switched transmission lines. Power will only flow for nanoseconds as the pulse travels over the line. There won't be a drop of 50% of the voltage at the target and no large power spikes in the unit or requirements for proper impedance matching at the receiver side. Some units like the thunderbolt look quite bad driving a 50 ohms transmission line, others that are designed with proper 50 ohms series impedance create a sharp nice signal. Bye, Said Sent from my iPad On May 14, 2012, at 17:21, Tom Van Baak t...@leapsecond.com wrote: Mark, I too once preferred 50% duty cycle 1 Hz signals because they seemed more natural. But one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. When a dozen DUT generate 1PPS along with as many REF pulses (via cascaded pulse distribution amps) and then these all go to both inputs of a TIC and there's also LED's on both TIC channels as well as the dist amps, the net load is enormous. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. Remember 5V into 50R is 0.1 Amps. That was a modest amount of current in the 1950's, but massive overkill today. So that's why I now prefer short (e.g., 1 ms or 10 us) pulses. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/15/2012 2:45 PM, shali...@gmail.com wrote: The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. But, since PPS is the leading edge, if the power draw for a longer pulse width causes timing problems, then a short pulse would too, unless the edge can somehow see into the future to know how long the pulse will last. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
seeing into the future for doing? Equalize the amplitude? Injecting/reducing the current to adjust the dV/dt? Can you explain? On Tue, May 15, 2012 at 9:47 PM, Mike S mi...@flatsurface.com wrote: On 5/15/2012 2:45 PM, shali...@gmail.com wrote: The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. But, since PPS is the leading edge, if the power draw for a longer pulse width causes timing problems, then a short pulse would too, unless the edge can somehow see into the future to know how long the pulse will last. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Yes, but the point is to not use end-termination for all the reasons mentioned by others in this thread, such as massive spike in power consumption once per second, over-voltage spikes if the termination is faulty or missing, higher ADEV due to power supply modulation, etc etc.. Your test clearly shows the ringing when the transmission line is left open, and it shows the massive current (5V into 50 Ohms) when end-terminating the cable. It also shows that the cable is ringing up to 7V or more! Which could actually kill your driver circuit by overvoltage if you forget to enable the 50 Ohms termination on your counter or scope for example. The voltage could theoretically spike all the way up to 10V as long as the pulse is traveling back on the coax. All more reasons why this is an undesirable mode of operation. To make this work without the unnecessary power consumption simply remove the end-termination resistor, and use it as the series termination resistor (R1 in your schematic)! Done. Attached are two plots of a series terminated (~55 Ohms) high-speed 1PPS transmission from our CSAC GPSDO board zoomed-in and zoomed-out to show the actual rise-time, and a longer time frame view. The 1PPS pulse was run through about 30 feet of LMR-195 cable, directly connected to the CSAC GPSDO 1PPS CMOS 5V output. There is no massive voltage over-shoot, the output is short-circuit protected, and no matching resistor is required, just a 50 Ohms coax cable. Use an additional 25 Ohm series resistance for 75 Ohms cables. The output rise time is 1.25ns at the end of the 30 foot cable, and the signal fully settles within 800ns, and never goes below 4V after the initial 1.25ns rise. The current spike on the power supply is only there during the time that the cable is being charged up, which is about 30 feet * 2 * 1.5ns/foot = ~100ns. That is short enough for the power supply caps to filter the current spike. In short, one could easily modify the Thunderbolt 1PPS output circuit which is probably a bunch of parallel AC240 gates with some low value series resistors, and modify these resistors to have the equivalent of 50 Ohms impedance. That would alleviate the need for end-termination on the coax, and provide very clean rise time, fall time, and no ringing. BTW: one advantage of this in the lab is that you can connect multiple instruments to one 1PPS output. The signal will take slightly longer to settle as it has to traverse and charge more cable hubs, but in the end there will be 5V on the cable with no DC current flowing, and there won't be any positive ringing above 5V. You cannot drive more than one input if you are using 50 Ohm end-termination without possibly over-loading the driver, and causing massive impedance mismatch, and getting the associated cable ringing etc. bye, Said In a message dated 5/15/2012 11:49:14 Pacific Daylight Time, shali...@gmail.com writes: The Thunderbolt's output impedance is much less than 10 ohms. However, it is only necessary to filter the end of the line for a clean pulse. See http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.php I used the Thunderbolt's PPS output as a source in those measurements. CSAC_risetime.GIFCSAC_risetime_zoom.GIF___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/15/2012 3:59 PM, Azelio Boriani wrote: seeing into the future for doing? Equalize the amplitude? Injecting/reducing the current to adjust the dV/dt? Can you explain? Once the leading edge has occurred, the only information of significance has been transmitted. What happens after doesn't matter. So what problem does a short pulse solve? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On Tue, 15 May 2012 15:47:46 -0400 Mike S mi...@flatsurface.com wrote: On 5/15/2012 2:45 PM, shali...@gmail.com wrote: The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. But, since PPS is the leading edge, if the power draw for a longer pulse width causes timing problems, then a short pulse would too, unless the edge can somehow see into the future to know how long the pulse will last. Not really. Keep in mind that you have capacitors everywhere. One or two small ones at the output driver directly. Maybe a few mid sized ones in the power distribution, if the device is a bit bigger. Bigger capacitors at the devices power supply, resp. power input. Even the mains socket can be regarded as a very very big capacitor. Each of these capacitors stores energy, proportional to its size (in Farad, i leave the Voltage dependence out for this). If the PPS pulse is short, it contains very little energy, which means the energy can be supplied by the small capacitors at the output driver. The longer the pulse gets, the more energy it needs. And the more energy it needs, the more capacitors further back in the power chain get involved. Which means that more subsystems of the device see the power spike of the output driver (and its assciated voltage drop). Which might have a negative effect on their performance. Now, why not place very big capacitors at the output driver? Because big capacitors are expensive, even more so fast and big capacitors. And you want to have very fast capacitors to have a sharp rising edge. As a rule of thumb, the frequency limit of a capacitor is inversly proportional to its size, if all other factors are kept the same. It is possible to use different materials or different build-ups which have better high speed properties, but these get very expensive very fast. So, the rising edge of the pulse, the one we usually look at, is determined by the output drivers slew rate and the fast capacitors that provide its energy. But the form of the rest of the pulse is determined by the power needs of the pulse and the size of the surrounding capacitors (and the impedance that leads to them). And keep in mind, that it's no use of having a fast rising edge, if the pulse colapses a couple ns later. Hope that explains it Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
It is worth noting that skipping the end termination is probably a bad idea when daisy-chaining a signal from one output to more than one device input. The input at the end of the cable will see a clean rise from zero to 5 V (or whatever the driver's open-circuit voltage is), but the other inputs along the length of the cable will not. They will see an initial rise from 0 to 2.5 V as the series termination at the driver and the cable impedance act as a voltage divider while the cable is being charged. Later, they will see another step change from 2.5 V to 5 V as the reflection returns from the open-circuit far end of the cable. If the input threshold is automatically set at half the input voltage swing, the input could trigger on the outbound or the reflected pulse, or even somewhere in between. This is in contrast to having a 50 ohm termination at the end of the cable (plus the 50 ohm series termination at the source), where all inputs along the length of the cable see a single edge transition from 0 to 2.5 V. They will each see the edge at a different time due to propagation delay, but all will see a clean edge. Dave On Tue, May 15, 2012 at 4:00 PM, saidj...@aol.com wrote: To make this work without the unnecessary power consumption simply remove the end-termination resistor, and use it as the series termination resistor (R1 in your schematic)! Done. Attached are two plots of a series terminated (~55 Ohms) high-speed 1PPS transmission from our CSAC GPSDO board zoomed-in and zoomed-out to show the actual rise-time, and a longer time frame view. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/15/2012 4:19 PM, Attila Kinali wrote: If the PPS pulse is short, it contains very little energy, which means the energy can be supplied by the small capacitors at the output driver. The longer the pulse gets, the more energy it needs. The pulse is meaningless. It's only the leading edge that matters. I understand how shorter pulses may make for marginally cheaper electronics. Which might have a negative effect on their performance. I might win the lotto. The question is exactly _how_ does it effect their performance, especially if they're synchronizing to the PPS signal. it's no use of having a fast rising edge, if the pulse colapses a couple ns later. Huh? If ns is too short, and ms is too long, what makes us just right? And why are there so many timing receivers that only output on the order of 20 us, when there are so many inputs which may require a few ms? PPS is edge triggered, not level triggered. Once the leading edge is transmitted (and it by necessity has a very fast rise time, so it looks to capacitors, transformers, etc. as a high frequency signal), the shape of the pulse really doesn't matter much. Some devices need more than a minimum above some threshold, but what ones need less than a maximum? If it doesn't look like a flat topped pulse, so what? As long as the decay is basically monotonic, and the receiver has some hysteresis (reasonable assumptions), it makes no difference. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Not really, your setup requires all inputs except the very last one to be high-impedance to work, and to have a trigger point of 1.25V as well to work properly (when used with a proper 50 Ohms source). So no difference there. So it doesn't make any difference, since the same exact inputs will work just as well with the open-ended circuit if the trigger point is set to 1.25V on those inputs. Same requirement for both setups. Daisy-chaining is a bad idea because you are getting the propagation delay between the different hubs as mentioned. Using a simple T with open-ended cables would make all inputs switch simultaneously if the cable lengths after the T are the same. Daisy chaining also creates stubs along the way due to the capacitive loading on the cable at the inputs, and the small amount of additional wiring at the stub, and these stubs will cause reflections going wild due to impedance mismatch at the stub, and run amok between stubs and between the ends of the cable. BTW: when setting the threshold to 2.5V and tapping-off somewhere in the cable, this is called reflected wave switching, as opposed to incident wave switching, which is what happens when you set the threshold to 1.25V. Also, the Thunderbolt has less than 5 Ohms output impedance, so you get a reflection going back from the 50 Ohms end-termination anyway because the impedance is mismatched! The signal won't stop at 2.5V, it will go all the way up to 5V in static conditions just the same as in my scenario. This can be seen in the plots that Didier had sent earlier. But worst of all: if your 50 Ohms end-termination falls off, or goes away because you turn-off that piece of equipment providing that termination, then almost sudden all of your inputs can see 10 Volts on the line, and could blow up due to overload. Having a 1.25V threshold input seeing a 10V signal is not a good idea.. You get all the drawbacks and more, and no real advantage. At least when connecting to e.g. a Thunderbolt output that has 50 Ohms series impedance. bye, Said In a message dated 5/15/2012 13:44:42 Pacific Daylight Time, dave.martind...@gmail.com writes: It is worth noting that skipping the end termination is probably a bad idea when daisy-chaining a signal from one output to more than one device input. The input at the end of the cable will see a clean rise from zero to 5 V (or whatever the driver's open-circuit voltage is), but the other inputs along the length of the cable will not. They will see an initial rise from 0 to 2.5 V as the series termination at the driver and the cable impedance act as a voltage divider while the cable is being charged. Later, they will see another step change from 2.5 V to 5 V as the reflection returns from the open-circuit far end of the cable. If the input threshold is automatically set at half the input voltage swing, the input could trigger on the outbound or the reflected pulse, or even somewhere in between. This is in contrast to having a 50 ohm termination at the end of the cable (plus the 50 ohm series termination at the source), where all inputs along the length of the cable see a single edge transition from 0 to 2.5 V. They will each see the edge at a different time due to propagation delay, but all will see a clean edge. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mike, Attila is trying to explain that the leading edge is not what we are concerned about in this thread (its subject to discussion in other email threads), it is the effect of what follows after that leading edge, and propagates down the power supplies to cause side effects that is being discussed here. Tom mentioned he can measure this as 10's of Watts of increased power consumption spikes on the AC line when the 1PPS goes high. This won't happen with short pulses, only with long ones that are end-terminated. In a message dated 5/15/2012 13:51:43 Pacific Daylight Time, mi...@flatsurface.com writes: On 5/15/2012 4:19 PM, Attila Kinali wrote: If the PPS pulse is short, it contains very little energy, which means the energy can be supplied by the small capacitors at the output driver. The longer the pulse gets, the more energy it needs. The pulse is meaningless. It's only the leading edge that matters. I understand how shorter pulses may make for marginally cheaper electronics. Which might have a negative effect on their performance. I might win the lotto. The question is exactly _how_ does it effect their performance, especially if they're synchronizing to the PPS signal. it's no use of having a fast rising edge, if the pulse colapses a couple ns later. Huh? If ns is too short, and ms is too long, what makes us just right? And why are there so many timing receivers that only output on the order of 20 us, when there are so many inputs which may require a few ms? PPS is edge triggered, not level triggered. Once the leading edge is transmitted (and it by necessity has a very fast rise time, so it looks to capacitors, transformers, etc. as a high frequency signal), the shape of the pulse really doesn't matter much. Some devices need more than a minimum above some threshold, but what ones need less than a maximum? If it doesn't look like a flat topped pulse, so what? As long as the decay is basically monotonic, and the receiver has some hysteresis (reasonable assumptions), it makes no difference. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/15/2012 5:14 PM, saidj...@aol.com wrote: it is the effect of what follows after that leading edge, and propagates down the power supplies to cause side effects that is being discussed here. I'm asking What side effects? I haven't seen any mentioned. And really, if an increase in power draw of 10 watts for an entire lab environment causes any problems, I'd question the quality of the power supplies, and ask what happens when you simply turn on the light? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
QED: here is a phase noise plot of a 200ms 1PPS pulse showing up in the phase noise spectrum of a 10MHz source (at 1Hz to 10Hz offsets) because the unit was providing a 100mA current pulses into the cable, and power supply modulation of the 10MHz output happened inside the unit. The pulses would likely not be visible if they had been only microseconds long, or the cable was not incorrectly end-terminated and causing the massive DC current to flow. Yes, yes, the unit could have been designed to handle that scenario, but the point is: modulation is going to happen, and could be 10's of Watts, and it will likely have some effect in one way or another. The discussion started with the question of why one would design short 1PPS pulses versus long pulses. This is one reason why. In a message dated 5/15/2012 14:24:07 Pacific Daylight Time, mi...@flatsurface.com writes: On 5/15/2012 5:14 PM, saidj...@aol.com wrote: it is the effect of what follows after that leading edge, and propagates down the power supplies to cause side effects that is being discussed here. I'm asking What side effects? I haven't seen any mentioned. And really, if an increase in power draw of 10 watts for an entire lab environment causes any problems, I'd question the quality of the power supplies, and ask what happens when you simply turn on the light? run94019-spec.gif___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Forgot to mention, on this list we are often concerned with noise floors of -170dBc or lower, and stabilities of 1E-013 or lower. At that level, your scenario of stepping into the room and turning on the light will likely cause a measurable effect just because of the mechanical vibration you are inducing into the crystal by walking into the room.. In a message dated 5/15/2012 14:24:07 Pacific Daylight Time, mi...@flatsurface.com writes: On 5/15/2012 5:14 PM, saidj...@aol.com wrote: it is the effect of what follows after that leading edge, and propagates down the power supplies to cause side effects that is being discussed here. I'm asking What side effects? I haven't seen any mentioned. And really, if an increase in power draw of 10 watts for an entire lab environment causes any problems, I'd question the quality of the power supplies, and ask what happens when you simply turn on the light? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
saidj...@aol.com said: Also, the Thunderbolt has less than 5 Ohms output impedance, so you get a reflection going back from the 50 Ohms end-termination anyway because the impedance is mismatched! I think that's a different problem. If the far end termination matches the cable there won't be any reflection. If the far end isn't terminated correctly, there will be reflections from the far end. There may also be reflections from joints in cables or a Tee and input load if you are daisy chaining multiple instruments. When those reflections get back to the typical low impedance driver, they will get reflected back again. It's not uncommon to use both source/series and end/parallel terminations. The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup. It also provides a current limit on the driver in case something gets shorted. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Yes, you are right of course. My bad. This should have been written as: The Thunderbolt has less than 5 Ohms output impedance, so if you get a reflection coming from the cable stubs or non-end-terminated cable back into the Thunderbolt, then you get ringing on the cable because the impedance is mismatched! On a properly series terminated device, any reflections on the open-ended cable coming back to the source will end in the sources' 50 Ohms terminator, and be removed. One more advantage I didn't mention for series termination versus the Thunderbolt used with end-termination. In a message dated 5/15/2012 15:03:12 Pacific Daylight Time, hmur...@megapathdsl.net writes: saidj...@aol.com said: Also, the Thunderbolt has less than 5 Ohms output impedance, so you get a reflection going back from the 50 Ohms end-termination anyway because the impedance is mismatched! I think that's a different problem. If the far end termination matches the cable there won't be any reflection. If the far end isn't terminated correctly, there will be reflections from the far end. There may also be reflections from joints in cables or a Tee and input load if you are daisy chaining multiple instruments. When those reflections get back to the typical low impedance driver, they will get reflected back again. It's not uncommon to use both source/series and end/parallel terminations. The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup. It also provides a current limit on the driver in case something gets shorted. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On Tue, 15 May 2012 16:51:13 -0400 Mike S mi...@flatsurface.com wrote: On 5/15/2012 4:19 PM, Attila Kinali wrote: If the PPS pulse is short, it contains very little energy, which means the energy can be supplied by the small capacitors at the output driver. The longer the pulse gets, the more energy it needs. The pulse is meaningless. It's only the leading edge that matters. I understand how shorter pulses may make for marginally cheaper electronics. It's not marginally, it's quite substantial. A 10nF capacitor can easily provide enough power for a 1-20us pulse (rough guestimate). For a 1ms pulse, you need a 1000 times larger capacitor, ie 10uF. The pulse rise times we want to acheive are 1ns, which means we have frequency components far into the GHz range. It is easy to find an 10nF capacitor that is good to a couple of GHz. Good luck in finding a 10uF that goes over 3MHz, and even these are not cheap at all. Yes, you can combine a 10nF and a 10uF so that the 10nF provides the energy for the edge and the 10uF the energy for the pulse, but this again is more difficult to do correctly [1]. You also have more than 1000 times higher capacitive loading to your power supply, which means you have to account for a roughly 1000 times higher rush in current, which makes your power supply at least 10 times more expensive. You have to choose a different driver that can handle the output power. And this driver is either a lot more expensive or slower, most likely both [2]. Or in short: there are quite a few compromises in the design of such a circuit. Each part has to fit to the others, or you will not acheive optimal performance. The big reason why we can have cheap rubidiums at home these days is not because they are build in large quantities and thus have become cheaper. No, it's because technological advances made it possible to do less or simpler compromises in the design, which made the device cheaper, and thus more devices got sold. Same goes for virtually any other high tech device you have in your home. Starting from your fridge, over your TV set up to your computer. Which might have a negative effect on their performance. I might win the lotto. The question is exactly _how_ does it effect their performance, especially if they're synchronizing to the PPS signal. We are measuring timing differences in the range of a couple of ps. This is faster than the rising time of the pulse you have. Ie the steepnes of the pulse is very important. Any modulation due to the power supply being a percent higher or lower will be visible in the measurements. And a percent variation is quite a good value for a normal power supply design with large load steps. Or think about your oscillator. Your power supply varies, this means the power supply of the oscillator varies too. This will ever so slightly (or not so slightly) modulate the drive strength of the oscillator which in turn will shift the frequency. And i'm not yet talking about the modulation that occurs on the EFC due to imperfect power supply rejection in the circuit that produces and processes the EFC. it's no use of having a fast rising edge, if the pulse colapses a couple ns later. Huh? If ns is too short, and ms is too long, what makes us just right? And why are there so many timing receivers that only output on the order of 20 us, when there are so many inputs which may require a few ms? If your capacitor is too small, it will only be able to provide the energy for the rising edge. After that, the capacitors further back have to support it. If they have a too high impedance, the voltage at the output driver will drop after the first edge. If the drop is too soon, the receiver of the pulse will not detect the first rising edge, but trigger on the second, washed out and slow edge. There are draw backs even if there is no drop, but a limit in the height the pulse reaches. If, due to too small capacitors, your pulse does not reach the full 5V, you have to use a smaller trigger voltage for your receiver. Which means you have a lower noise marign (the output and input noise voltages are often independent of drive strength). This in turn means you have more jitter on your pulse on the receiver side. Which will limit the resolution you get for your instruments. PPS is edge triggered, not level triggered. Yes, but the receiver has a minimum length requirement for the pulse, otherwise it will not see it. Or even worse, it will not trigger correctly and might enter a metastable state, which can lead to: 1) a delay of several ms (yes, miliseconds!) until the device correctly triggers, 2) high current consumption within the receiver due to high and low side transistors conducting at the same time, which in turn will lead to heating and might in the worst case destroy the receiver, in the best case you just have degraded performance due to higher thermal noise. Once the leading edge is transmitted (and it by necessity has a
Re: [time-nuts] Why are 1PPS signals so skinny?
On Wed, 16 May 2012 00:40:07 +0200 Attila Kinali att...@kinali.ch wrote: Just have a look at [3]. The spurs you see there are most likely * 60Hz mains * 120Hz mains (first harmonic) * a nearby radio station (according to TVB) Err.. sorry, this should read John Ackermann, not TVB. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On May 14, 2012, at 09:33 , b...@lysator.liu.se wrote: More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Is a similar standard available for the older PLGR devices? -- Mark J. Blair, NF6X n...@nf6x.net http://www.nf6x.net/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Jenny Craig? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
saidj...@aol.com wrote: Yes, but the point is to not use end-termination for all the reasons mentioned by others in this thread, such as massive spike in power consumption once per second, over-voltage spikes if the termination is faulty or FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On Tue, 15 May 2012 16:43:50 -0700, Rick Karlquist rich...@karlquist.com wrote: saidj...@aol.com wrote: Yes, but the point is to not use end-termination for all the reasons mentioned by others in this thread, such as massive spike in power consumption once per second, over-voltage spikes if the termination is faulty or FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Rick Karlquist N6RK One of the papers I read about implementing high performance FPGA delay time counters mentioned the heartbeat LED causing a significant amount of additional jitter. I have always buffered such signals (for other reasons as well like ESD resistance) and used separate power and ground paths for the high current loop. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 05/16/2012 01:43 AM, Rick Karlquist wrote: saidj...@aol.com wrote: Yes, but the point is to not use end-termination for all the reasons mentioned by others in this thread, such as massive spike in power consumption once per second, over-voltage spikes if the termination is faulty or FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. The TDR blinking light on Tek SD-24 caused significant delay shifts. An upgraded firmware removed blinking to lower jitter. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
The issue is that the overall power drawn at 1Hz can cause stability problems for all the power supplies, so in the example given by Tom, the power modulation probably affected the power supplies regulation and it affected the next pulse, not the first pulse. Since it is continuous pulse train, the perturbation affects potentially all the pulses. This page shows the spectrum of pulses of constant frequency and amplitude, but varying width: http://www.ko4bb.com/Test_Equipment/Pulse_Modulation/ You can see that when the duty cycle is changed from 10 to 50%, the amplitude of the first harmonic (the fundamental) goes up by 10dB. So if you are only interested in the leading edge and there is appreciable power spent when the pulse is high, a longer pulse only draws more power at the fundamental without adding anything to the precision of the leading edge. If the fundamental is 1Hz, you will pulse the power drawn from the source at 1Hz, which is too low to be filtered out by most power supplies Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mike S mi...@flatsurface.com Sender: time-nuts-boun...@febo.com Date: Tue, 15 May 2012 15:47:46 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 5/15/2012 2:45 PM, shali...@gmail.com wrote: The narrow pulses are easily filtered by the power supply because the frequency distribution of the power consumption has a much smaller component at 1Hz. But, since PPS is the leading edge, if the power draw for a longer pulse width causes timing problems, then a short pulse would too, unless the edge can somehow see into the future to know how long the pulse will last. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mike, here is the effect of the A/C cycling on and off during a warm spring day on the delay through a piece of RG-8 cable maybe 3 feet long: http://www.ko4bb.com/Test_Equipment/data/HP10811-raw.png The full scale (screen height) is about 5x10 to the -10, the length of the record was about one hour. The cable was very short, I did not record the temperature variation but it was maybe 2F. You can imagine what a 100W light bulb (or a warm body) might do if you try to measure at 10 to the -12, and/or you have longer cables. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mike S mi...@flatsurface.com Sender: time-nuts-boun...@febo.com Date: Tue, 15 May 2012 17:23:41 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? On 5/15/2012 5:14 PM, saidj...@aol.com wrote: it is the effect of what follows after that leading edge, and propagates down the power supplies to cause side effects that is being discussed here. I'm asking What side effects? I haven't seen any mentioned. And really, if an increase in power draw of 10 watts for an entire lab environment causes any problems, I'd question the quality of the power supplies, and ask what happens when you simply turn on the light? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Hi Rick, one reason why we happy blink at 1/2Hz :) There are other offendors as well, such as the processor and GPS going through the hoops once per second, but the 100mA surge from the 1PPS output driver trumps all else. bye, Said In a message dated 5/15/2012 16:44:08 Pacific Daylight Time, rich...@karlquist.com writes: saidj...@aol.com wrote: Yes, but the point is to not use end-termination for all the reasons mentioned by others in this thread, such as massive spike in power consumption once per second, over-voltage spikes if the termination is faulty or FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
I met Jenny in 1987 - not that skinny at the time :) That was after she sold the company already. In a message dated 5/15/2012 16:41:34 Pacific Daylight Time, b...@iaxs.net writes: Jenny Craig? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Absolutely, that's what the pictures I linked to earlier show, particularly the last one. It is sufficient to properly terminate one end to eliminate ringing, as long as you have no tees in line. There may be specific reasons why it is preferable to terminate one end rather than the other, like protecting the driver. In any case, if the pulse is narrow, the risk of damage to the driver because of short to ground is also greatly reduced. In my experience, I prefer to terminate the end because it tends to reduce the noise sensitivity at the receiver (not just for timing, but for anything where noise is critical). If the amplitude is too great, I put a matched divider at the end. I always try to have as much signal amplitude on the cable as possible to improve the S/N ratio. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Hal Murray hmur...@megapathdsl.net Sender: time-nuts-boun...@febo.com Date: Tue, 15 May 2012 15:02:36 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Why are 1PPS signals so skinny? saidj...@aol.com said: Also, the Thunderbolt has less than 5 Ohms output impedance, so you get a reflection going back from the 50 Ohms end-termination anyway because the impedance is mismatched! I think that's a different problem. If the far end termination matches the cable there won't be any reflection. If the far end isn't terminated correctly, there will be reflections from the far end. There may also be reflections from joints in cables or a Tee and input load if you are daisy chaining multiple instruments. When those reflections get back to the typical low impedance driver, they will get reflected back again. It's not uncommon to use both source/series and end/parallel terminations. The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup. It also provides a current limit on the driver in case something gets shorted. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/15/2012 8:58 PM, shali...@gmail.com wrote: Mike, here is the effect of the A/C cycling on and off during a warm spring day on the delay through a piece of RG-8 cable maybe 3 feet long: You're comparing the effect of voltage droop due to a 10W load on a 120V (or 240V, for Euros) AC feed with the temperature cycling plus voltage droop due to a 1000W+ HVAC unit? (Was your RG-8 in a separate climate enclosure? Or might you be including source/sink changes in your measurement?) Not only is 10W on a AC power feed pretty insignificant, but unless you're receiving a separate circuit from the substation, the building (or neighbor's) HVAC cycling will have more effect. All other comments have been unique to the performance of individual devices, not the propagation of PPS through a lab. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
For what it's worth, that seems to be the standard way to distribute analog video (composite or component). A low-impedance voltage source with a gain of 2 drives a bunch of outputs with an individual 75 ohm series resistor for each output. Each cable that is connected to an output has a parallel 75 ohm terminator at the far end. Inputs are all high impedance. The result is cables properly terminated at both ends (no reflections), unity gain overall (the driver gain of 2 compensates for the 2:1 voltage divider due to the terminators, and the ability to daisy-chain through several inputs. - Dave On Tue, May 15, 2012 at 6:02 PM, Hal Murray hmur...@megapathdsl.net wrote: It's not uncommon to use both source/series and end/parallel terminations. The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup. It also provides a current limit on the driver in case something gets shorted. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
rich...@karlquist.com said: FWIW, the E1938A oscillator control board had a happy light LED that flashed 1 time per second, and sure enough this corrupted the power supply and affected some applications. We added a command to turn it off. Why should lights blink when they are happy? Your eye is real good at noticing blinking things. Why not use blinking for things that are broken and need attention? Of course, with a PPS, blinking is an obvious thing to do: 1 resistor, 1 LED, your eye does all the work. I built a converter from blink on happy to blink on sad. I've been happy with it. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Feed a 5V 1Hz square wave into a 50OHM load and look at the power drain. Do the same with a 100uS pulse and smile at the difference. On Mon, May 14, 2012 at 5:23 PM, Mark Sims hol...@hotmail.com wrote: My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Le 14/05/2012 17:23, Mark Sims a écrit : My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. NAVMAN Jupitr-T26 ms ONCORE VP ~200ms UT+200ms M12T 1PPS 200ms 100Hz 2-3ms these are all timing receivers and the signals will trip serial receivers without pulse stretching.. So the picture is not that gloomy. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? -- Björn Feed a 5V 1Hz square wave into a 50OHM load and look at the power drain. Do the same with a 100uS pulse and smile at the difference. On Mon, May 14, 2012 at 5:23 PM, Mark Sims hol...@hotmail.com wrote: My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
I thought it was only standard practice, now I see that there are standards and requirements too. On Mon, May 14, 2012 at 6:33 PM, b...@lysator.liu.se wrote: Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? -- Björn Feed a 5V 1Hz square wave into a 50OHM load and look at the power drain. Do the same with a 100uS pulse and smile at the difference. On Mon, May 14, 2012 at 5:23 PM, Mark Sims hol...@hotmail.com wrote: My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
You don't want it symmetric. If it were then you'd not be able to notice if it was inverted. You need the asymmetry but the next question is how asymmetric? In theory all the information is on the raising edge of the pulse so you cam make it as short as you like and not loose any information.OK so that sets the limits on both ends.Next thing, I'd guess is power, a low duty cycle certainly uses less power. On Mon, May 14, 2012 at 8:23 AM, Mark Sims hol...@hotmail.com wrote: My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mark Sims wrote: My first inclination, if I were building a timing receiver, would be to make the PPS output a nice, symmetrical square wave. But pretty much all GPS timing receivers output an anorexic, dinky little heroin addicted supermodel sized pulse (from 1 to 150uS wide is typical). ___ One reason might be that it is convenient to have AC coupled hardware, with a reasonable low frequency cutoff. 1 Hz is not a reasonable low frequency cutoff, which is what you would need if a square wave were used. (Actually, to accurately reproduce a 1 Hz square wave requires response down to .1 Hz and preferrably .01 Hz, due to droop and phase shift distortion issues). A short pulse will conveniently propagate though the same sort of distribution amplifiers used for 10 MHz, 5 MHz, 100 kHz, etc. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mark, Azelio and Björn, On 05/14/2012 06:33 PM, b...@lysator.liu.se wrote: Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? You need to look at MIL STD 188/155 which if I recall things was initially formed in the 60thies. An AccuBeat presentation actually says that the PPS was originally defined in it. The MIL STD 188/155 is actually a 10 V peak level, so it was much hotter than we are used to know. It specified 5 MHz as base frequency, or power of 2 multiples (10, 20, 40 MHz... ). It was later reformulated in the PTTI spec, which ICD GPS 060 is a derivate. The 50 ns rise and 1 us fall slopes comes from that spec. I was not able to find MIL STD 188-155 on the net right now, but I have been able to download it before, so if someone is a more lucky it should surface. I should have my download somewhere. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
OK, thank you for the references. On Mon, May 14, 2012 at 9:20 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Mark, Azelio and Björn, On 05/14/2012 06:33 PM, b...@lysator.liu.se wrote: Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? You need to look at MIL STD 188/155 which if I recall things was initially formed in the 60thies. An AccuBeat presentation actually says that the PPS was originally defined in it. The MIL STD 188/155 is actually a 10 V peak level, so it was much hotter than we are used to know. It specified 5 MHz as base frequency, or power of 2 multiples (10, 20, 40 MHz... ). It was later reformulated in the PTTI spec, which ICD GPS 060 is a derivate. The 50 ns rise and 1 us fall slopes comes from that spec. I was not able to find MIL STD 188-155 on the net right now, but I have been able to download it before, so if someone is a more lucky it should surface. I should have my download somewhere. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Magnus, https://assist.daps.dla.mil/quicksearch/ is the search site for military standards. MIL-188-155 is not found. Could it be another dash number? Mike On 5/14/2012 2:20 PM, Magnus Danielson wrote: Mark, Azelio and Björn, On 05/14/2012 06:33 PM, b...@lysator.liu.se wrote: Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? You need to look at MIL STD 188/155 which if I recall things was initially formed in the 60thies. An AccuBeat presentation actually says that the PPS was originally defined in it. The MIL STD 188/155 is actually a 10 V peak level, so it was much hotter than we are used to know. It specified 5 MHz as base frequency, or power of 2 multiples (10, 20, 40 MHz... ). It was later reformulated in the PTTI spec, which ICD GPS 060 is a derivate. The 50 ns rise and 1 us fall slopes comes from that spec. I was not able to find MIL STD 188-155 on the net right now, but I have been able to download it before, so if someone is a more lucky it should surface. I should have my download somewhere. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 2012/05/14 18:02, time-nuts-requ...@febo.com wrote: https://assist.daps.dla.mil/quicksearch/ is the search site for military standards. Hmm. Doesn't find MIL-TGDBP-41. I got this from my (now late) great uncle, Bob Sedgwick -- who was to hydraulics what I am to computers, only he has a number of patents. Some smart-aleck at Wright Field, as it then was, put this on a drawing, and it went without comment for quite a while until someone tried to look it up. This escalated to a bird colonel, who then tracked down the miscreant. It stands for Make It Like The G-D Blueprint For Once. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Maybe the correct number is MIL-STD-188-115? On Tue, May 15, 2012 at 1:18 AM, Jim Hickstein j...@jxh.com wrote: On 2012/05/14 18:02, time-nuts-requ...@febo.com wrote: https://assist.daps.dla.mil/quicksearch/ is the search site for military standards. Hmm. Doesn't find MIL-TGDBP-41. I got this from my (now late) great uncle, Bob Sedgwick -- who was to hydraulics what I am to computers, only he has a number of patents. Some smart-aleck at Wright Field, as it then was, put this on a drawing, and it went without comment for quite a while until someone tried to look it up. This escalated to a bird colonel, who then tracked down the miscreant. It stands for Make It Like The G-D Blueprint For Once. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
I haven't heard that one before. I try to slip in the TLAR check in all the test procedures I write. When 'they' ask, I look at it and say: That Looks About Right. Mike On 5/14/2012 6:18 PM, Jim Hickstein wrote: On 2012/05/14 18:02, time-nuts-requ...@febo.com wrote: https://assist.daps.dla.mil/quicksearch/ is the search site for military standards. Hmm. Doesn't find MIL-TGDBP-41. I got this from my (now late) great uncle, Bob Sedgwick -- who was to hydraulics what I am to computers, only he has a number of patents. Some smart-aleck at Wright Field, as it then was, put this on a drawing, and it went without comment for quite a while until someone tried to look it up. This escalated to a bird colonel, who then tracked down the miscreant. It stands for Make It Like The G-D Blueprint For Once. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Hi I would bet that the basic electrical definition of the skinny PPS dates at least to the mid 50's if not earlier. Bob On May 14, 2012, at 3:20 PM, Magnus Danielson wrote: Mark, Azelio and Björn, On 05/14/2012 06:33 PM, b...@lysator.liu.se wrote: Mark Azelio, Or even 10V into 50ohm, 20us... See figure 3-4 in ICD-GPS-060. http://www.navcen.uscg.gov/pdf/gps/ICD-GPS-060B.pdf More modern 3-5.5V into 50ohm, 20us. http://contracting.tacom.army.mil/majorsys/jab/DAGR%20Interface%20Specification.pdf Above are two standards demanding short skinny 1PPS pulses. Are there any other standards with distinct shape requirements on 1PPS pulses? You need to look at MIL STD 188/155 which if I recall things was initially formed in the 60thies. An AccuBeat presentation actually says that the PPS was originally defined in it. The MIL STD 188/155 is actually a 10 V peak level, so it was much hotter than we are used to know. It specified 5 MHz as base frequency, or power of 2 multiples (10, 20, 40 MHz... ). It was later reformulated in the PTTI spec, which ICD GPS 060 is a derivate. The 50 ns rise and 1 us fall slopes comes from that spec. I was not able to find MIL STD 188-155 on the net right now, but I have been able to download it before, so if someone is a more lucky it should surface. I should have my download somewhere. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Mark, I too once preferred 50% duty cycle 1 Hz signals because they seemed more natural. But one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. When a dozen DUT generate 1PPS along with as many REF pulses (via cascaded pulse distribution amps) and then these all go to both inputs of a TIC and there's also LED's on both TIC channels as well as the dist amps, the net load is enormous. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. Remember 5V into 50R is 0.1 Amps. That was a modest amount of current in the 1950's, but massive overkill today. So that's why I now prefer short (e.g., 1 ms or 10 us) pulses. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
On 5/14/2012 8:21 PM, Tom Van Baak wrote: one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. How does a short pulse help? It's still tens of watts every second, but instead of lasting 0.5 seconds, it lasts 0.5 seconds. Less power used overall, but still the same sudden change on the second. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
Hi If you want to avoid a crazy power supply, you decouple the power to the output amplifier on the PPS driver. Nice big caps, droop a little during the pulse. Charge up while there's no pulse. Bob On May 14, 2012, at 8:44 PM, Mike S wrote: On 5/14/2012 8:21 PM, Tom Van Baak wrote: one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. How does a short pulse help? It's still tens of watts every second, but instead of lasting 0.5 seconds, it lasts 0.5 seconds. Less power used overall, but still the same sudden change on the second. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Why are 1PPS signals so skinny?
These types of pulses should be routed as open-ended source-terminated reflected wave switched transmission lines. Power will only flow for nanoseconds as the pulse travels over the line. There won't be a drop of 50% of the voltage at the target and no large power spikes in the unit or requirements for proper impedance matching at the receiver side. Some units like the thunderbolt look quite bad driving a 50 ohms transmission line, others that are designed with proper 50 ohms series impedance create a sharp nice signal. Bye, Said Sent from my iPad On May 14, 2012, at 17:21, Tom Van Baak t...@leapsecond.com wrote: Mark, I too once preferred 50% duty cycle 1 Hz signals because they seemed more natural. But one day during an experiment where I was comparing a large set of clocks I noticed my lab's digital AC power meter was jumping by tens of watts every second. When a dozen DUT generate 1PPS along with as many REF pulses (via cascaded pulse distribution amps) and then these all go to both inputs of a TIC and there's also LED's on both TIC channels as well as the dist amps, the net load is enormous. The last thing you want in a precision timing lab is to load your AC line down exactly once a second. Remember 5V into 50R is 0.1 Amps. That was a modest amount of current in the 1950's, but massive overkill today. So that's why I now prefer short (e.g., 1 ms or 10 us) pulses. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
